Process Engineering Consulting

DI – Water plants – Closed circular piping

Water is an important source and auxiliary material in the production of cosmetic and pharmaceutical products. It also serves as a rinsing aid for CIP cleaning of the product-contacting surfaces of the plant components and the pipelines. Water systems are therefore among the key systems in the production process of products.

The different branches of industry have different water requirements.

General terms for water qualities:

  • DI - Water (fully demineralised / deionised water
  • WFI - Water for Injection
  • PW - Purified Water
  • HPW - Highly Purified Water

The level of purity of demineralised water is mostly determined by measuring the electrical conductivity of the water µS/cm, by means of conductivity measuring devices.

Mode of operation of generating water using the reverse osmosis procedure

Reverse osmosis is used to substantially remove dissolved components of the available raw water. In the case of high calcium content in the raw water, the use of an upstream softening plant is recommended. All water treatment plants start with a filtration stage: Multi-level filters, candle filters (with depth effect) or, more recently, ultrafiltration and microfiltration systems are used in the case of particulate pollution or turbidity. After this first purification step, a number of further processes are available with which certain water constituents can be removed. By means of active carbon filters, for example, oxidization agents can be reduced or low molecular organic impurities can be absorbed and thus removed from the water.
In a softening plant, calcium (Ca2+) and magnesium (Mg2+) or also metals like bivalent iron are replaced by sodium ions (Na+). With the large inner surface of the resin bed, softening is the most microbiologically critical element of the entire processing chain. Chemical disinfection during the regeneration keeps the germ counts at a tolerable level. Today, plants which are can be sanitised with hot water are increasingly being given preference. In modern water treatment plants, reverse osmosis is the process of choice for desalinisation. This can be attributed to the numerous advantages over ion exchangers. Reverse osmosis, a membrane process, is both a mechanical and chemical filtration process. In this process, the feed water is forced through the semi-permeable membrane at a higher pressure than the osmotic pressure and thereby divided into a concentrate flow containing the separated salts and other impurities and a permeate flow (pure water with a very low salt content). The membranes of reverse osmosis are extremely sensitive to fouling, scaling and oxidization agents. With reverse osmosis, excellent separation rates for salts, particles, micro-organisms, pyrogens and other ingredients can be achieved. In order to achieve the required conductivity of the pure water, a second stage or an electro-deionisation plant /EDI) is connected downstream, which provides a lower residual salt content and thus an improved safety margin to the limit values.

Closed circular pipelines to the extraction points

Closed circular pipelines are used between the storage tank and the extraction points; this is necessary to avoid germination caused by standing water. The circular piping system leads past all extraction points and the water reaches the consumers via manual or automatic valves.

The pipelines are composed of the following materials:

  • PVDF (only chemical “sanitisation“ only)
  • Stainless steel (can be sterilised) - 1.4404 / 1.4435 (316L)

Pipeline surfaces in contact with water:

  • Ra < 0.8 μm
  • WFI - lines  0.6 – 0.4 electro-polished, according to customer requirements

All components are connected to one another in compact design and virtually dead leg- free. All areas must be constructed in such a way that they are rinsed. Connections with seal offset/thread etc. in the closed circular pipeline are to be avoided. Preferably, “sterile connections” pursuant to DIN 11864 should be used. Where hot – cold changes occur, sterile flange connections are to be used wherever possible. At the extraction points, low dead leg T-membrane valves are to be employed, so that no germs can be formed due to standing water. The sealing materials must be approved by the FDA (Food and Drug Administration). A passivation is recommended after completion of the closed circular pipelines and the plant components.

UV - Treatment

UV is often used to keep water free of germs. In the case of UV disinfection or also UV Sterilisation, the water is irradiated with ultra-violet light. UV disinfection is widely used as a bactericide in water treatment. The UV light destroys the DNA, the cell membranes and the enzymes of the microorganisms by building free radicals in the water. The process takes place by the pre-treated water flowing through an irradiation chamber. UV radiation with a wavelength of 254 nm is the strongest for the anti-bacterial effect. The effectiveness is improved by the most turbulent possible flow in the UV disinfection.

Further sterilisation takes place by sanitisation or SIP processes, which are to be carried out in prescribed cycles. It must be pointed out here that the plants must be designed for the appropriate sterilisation processes.

Sanitisation 80°C

In order to ensure problem-free operation of a DI water plant, this should be sanitised at least 4 x per year. Sanitisation is usually carried out by heating the DI water by means of a heat exchanger. For the sanitisation process, the water in the tank and in the pipeline is heated to 80°C. As soon as all points within the tank and the pipeline network are heated to 80°, the hot water is circulated for one hour. Subsequently, the system is emptied and the tank and circuit are refilled with cold water to complete the sanitisation process.  This process can be fully automated.

Pressurised hot water - sterilisation 110 - 130°C

The process of pressurised water sterilisation is similar to sanitisation. The primary difference is that this process is operated at higher temperatures and thus the DI water system must be designed accordingly as, in addition to the increased pumping pressure in the pipeline and in the container, an excess pressure can build up due to evaporation of water above 100°C. At a water temperature of 110°C, a steam pressure of 0.5 bar is generated during sterilisation. At a water temperature of 121°C, there is already a steam pressure of 2 bar. When the temperature in the container reaches 100°C, the air in the interior is displaced by the resulting steam pressure. After the air has escaped, the ventilation valve on the sterile filter is closed so that the steam pressure and thus the intended temperature builds up and is maintained over a certain period of time.
The process can be carried out automatically, as with sanitisation.

Sterilisation with ultra-pure steam

Sterilisation with ultra-pure steam requires a higher investment expenditure as the design of the plant components must meet the higher requirements (z. B. AD 2000 - Regulations/EN ISO 17665-1:2006 (D), as well as a comprehensive qualification and validation of the plant components).
For the ultra-pure sterilisation process, all plant components must be emptied.  Steam traps with suitable non-return valves must be installed at the extraction points and at the lowest points of the pipeline. The condensate must be dissipated safely. It must be ensured that people cannot injure themselves on the hot pipes.  In order to safely vent the system, it is recommended that the storage tank and the pipeline network be placed under vacuum to evacuate the air. After venting, the temperature can be regulated by an inflow of ultra-pure steam, depending on the pressure.   Care should be taken that the pipelines are also connected to the steam network and thus a steam flow through to the condensate drain-off point is ensured. Temperature sensors, which measure temperatures and adjust the steam according to the pressure, are to be installed at the points that are difficult to sterilise and at the condensate drain-off points. After reaching the defined sterilisation temperature at all sensors (e.g. 121°C or higher), the established sterilisation time begins.
The basic prerequisite for this is that:

The sterilisation processes must be reproducibly controllable. The quality-relevant measured values of the sterilisation processes must be recorded and documented. The sterilisation process should be fully automatic.

Appropriate SOPs must be prepared for handling individual sterilisation procedures.

Heating of water circuits

The heating of a water circuit can take place by means of a tube bundle heat exchanger.  In order to avoid microbial contamination, care should be taken that the water temperatures for storage are between 70°C and 99°C. Cold water should be stored at approx. <18°C, in order to avoid germs in the storage tank. The storage of the cooling water at less than 18°C can be via a heat exchanger in the closed circular pipeline.

Qualification of water plants

In order to meet the GMP requirements for water plants, a qualification is required:

  • RA – Risk Analysis
  • DQ – Design Qualification
  • IQ – Installation Qualification
  • CAL - Calibration
  • OQ – Operational Qualification
  • PQ – Performance Qualification
  • R - Report

The qualification work should be specified neatly in the requirement specifications.

SEEFRIED Verfahrenstechnik GmbH can be of help to you in the design of the system/plant, as well as with the qualification.